1. Field of the Invention
The present invention relates to an apparatus and a method for a channel feedback in a Multiple Input Multiple Output (MIMO) system, and more particularly, to an apparatus and a method for a channel feedback in a MIMO system, which reduces an overhead of a channel feedback and an amount of a pilot in a multiple antenna system of which a spatial correlation is comparatively high.
2. Description of the Related Art
To meet the demand for wireless data traffic which has increased since deployment of 4G communication systems, efforts have been made to develop an improved 5G or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a “Beyond 4G Network” or a “Post LTE System.”
The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, beamforming, massive Multiple-Input Multiple-Output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, analog beamforming, and large scale antenna techniques are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, Device-to-Device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation and the like.
In a 5G system, Hybrid Frequency Shift Keying (FSK), Quadrature Amplitude Modulation (QAM), Feher's QAM (FQAM) and Sliding Window Superposition Coding (SWSC), as an Advanced Coding Modulation (ACM), and Filter Bank Multi Carrier (FBMC), Non-Orthogonal Multiple Access (NOMA), Sparse Code Multiple Access (SCMA), and Low-Density Parity-Check (LDPC) coding, as an advanced access technology, have been developed.
Recently, in order to transmit high quality data at a high speed in a wireless communication environment, research on a Multiple Input Multiple Output (MIMO) system which uses resources of a spatial area is actively being performed. Specially, interest in a massive MIMO technique which uses several tens to several hundreds of antennas in a base station is increasing.
The massive MIMO system may install a plurality of antennas in, for example, a Base Station (BS), and may relatively easily resolve various problems such as fast fading and inter-user interference by using only a simple linear precoder. In addition, the massive MIMO system may obtain a relatively high data rate. Advantages of the massive MIMO system include the number of antennas supported by the BS is not limited, and it is based on an assumption that the BS is aware of all channel information for each antenna supported by the BS.
The MIMO system may be classified into a Single-User MIMO (SU-MIMO) method in which a user uses all of the identical time and space resources and a Multi-User MIMO (MU-MIMO) method in which a plurality of users share all of the identical time and space resources.
The SU-MIMO method has been discussed in several standards such as Institute of Electrical and Electronics Engineers (IEEE) 802.16, because a method for transmitting a principal singular vector of a channel such as a Grassmannian codebook by quantizing the principal singular vector of the channel for a channel feedback has been developed.
Since cooperation between users is almost impossible using the MU-MIMO method, interference between receivers (i.e., users) should be removed or relieved by using only a precoder. In order to generate a precoder supporting multiple users in a BS, each receiver should feed channel information back to the BS.
A feedback method in the MU-MIMO system includes an orthogonal beamforming method and a vector quantization method.
The orthogonal beamforming method is a method in which a receiver selects a Precoding Matrix Index (PMI) and feeds the PMI back to a BS.
The vector quantization method is a method in which a receiver selects a Channel Direction Index (CDI) and feeds the CDI back to a BS.
The lower the number of receivers which can simultaneously support the orthogonal beamforming the more advantageous, and thus a method for feeding back a PMI to the BS has been described.